1. Field of the Invention
The present invention relates to improvements in the performance of coated fire barrier fabrics in contact with smoldering fires.
2. Description of the Prior Art
The term "upholster" means to fit out with covering material, padding, springs, etc., and is generally used in connection with furniture. The covering material, or face fabric, and fittings used to attach these materials to furniture, and the like, is commonly referred to as "upholstery".
Upholstery materials, primarily the covering material and padding have often been the site for propagation of fire from sources such as smoldering cigarettes and the like.
In order to contain and control smoldering fires in upholstered furnishings, specific configurations of flame resistant fabrics have been used as fire barriers interposed between the outer covering material and the filling materials. Such barriers envelop and contain the filling materials completely.
U.S. Pat. No. 4,690,859 to Porter et al., discloses the prevention of open flame combustion of upholstery filling material by controlling the porosity of the fabric to less than 200 cubic feet per minute of air per square foot, measured at room temperature at one-half inch of water pressure. It is believed that maintaining this parameter prevents sufficient oxygen flow to the filling or padding that is necessary to sustain combustion.
In general, upholstery materials exposed to high heat fail by two mechanisms. The first mechanism is where high external heat flux drives the pyrolysis of the filling material to combustion despite the containment provided by the barrier. A second failure mechanism occurs from the low oxygen demand of a smolder, that is, where burning and smoking occur without flame, and an object is consumed by slow combustion. It has been found that the low oxygen demand of a smolder can require an air supply as low as 0.1 cubic feet of air per minute.
A simple solution to the problem of controlling a smoldering fire in the outer upholstery fabric is to coat the fabric in a manner which renders it impermeable, thereby preventing the smolder site from reaching the padding or filling material. A drawback of this approach is that an enclosure such as a pillow or cushion covered with an impermeable fabric has an objectionable balloon-like feel unless some level of porosity is imparted to it.
Some approaches utilize ventilation ports as part of the construction of the pillow fabric, thereby allowing the use of non-porous materials such as vinyl chloride, which simulate leather.
The porosity of a porous fabric can be maintained to an extent by coating the fabric with a foamed latex base, or by using an unfoamed paste at limited add on, or by producing an impermeable coating followed by subsequent mechanical treatment, such as needling, to produce holes in the coating.
In general, the problem of extingusshing a smoldering fire is first addressed by draining the heat from the smolder area and/or by insulating the major fuel supply from the upholstered material, specifically the filling or padding, from the ignition source. A successful approach in extinguishing a smoldering fire can also provide improved performance in an open flame or high heat flux scenario.